Free Server Monitoring Software

I work as a network administrator. I have a lot of servers that I am in charge of. I have been looking for a decent ping based network monitor that will watch all of my servers and routers. Today I found DreamSys Server Monitor. Finally, this is what I have been wanting. I have linked Windows servers, Novell servers, and Cisco routers in this software, and it is doing a great job. I see each server listed on my monitoring system at all times. It is defaulted to ping check all these servers every minute. When there is a problem, the server goes red. I have an alert WAV sound file play. It then can send an email, which will go to my blackberry. So, what is the total cost of this software? FREE FREE FREE. I love it when I find something I like for free. If you are in charge of a number of servers, give DreamSys Server Monitor a try.